“Tell him not to talk. And not to write to my mother describing acts of anal sex under any circumstances whatsoever.”

Ah, the perils of taking a younger lover. So malleable in some ways (“Hop on to all fours, there’s a good chap. That always works best, don’t you think?”) and so thoroughly wayward in others.

Most times, both parties manage to extricate themselves and walk away unharmed. Things are trickier, alas, if you are the new Liberal leader, set fair to transform your party from cranky, faddist, po-faced no-mark into legitimate power player, and tear asunder the duopoly enjoyed by the Tories and Labour for half a century by a blessed concatenation of political circumstances and the sheer force of your wickedly clever, devilishly funny, perennially media-ready personality.

Such is the problem facing Jeremy Thorpe by the end of the opening episode of Russell T Davies’s frankly brilliant A Very English Scandal – a three-part dramatisation of events leading up to Thorpe’s infamous 1979 trial for conspiracy to murder his troubled and increasingly troublesome young boyfriend, Norman Scott.

Hugh Grant plays Thorpe and – clearly having the time of his actorly life – is revelatory. Charming, sly, duplicitous, forthright, manipulative, sometimes by turns, sometimes all at once, he is never less than wholly convincing and compelling. Everything (bar the stutter) that made him a romcom star is still there, but now there is everything else too. He handles the comic scenes and moments, which are sprinkled liberally throughout, with the deftness you’d expect, but never loses sight of the underlying nervousness, fear and venality underlying the politician’s moves. Discussing with best friend Peter Bessell (Alex Jennings, brilliant as a devotee with a shadow on his soul) his need to marry in order to progress in politics (“You’ll need to find a girl who’s led … a sheltered life”), he is part shark – always moving forward lest he founder and die – and part snake, shedding old skins and growing new ones as the moment dictates, and always so wry and rogueish with it that you find yourself thinking that whoever she turns out to be, she could do worse. You might not have a lot of sex, but you would have an endlessly good time.

Poor, unstable, neurotic Norman – born Josiffe, renamed Scott when he relocates to Dublin and a modelling career seems to be taking off – is played with his customary delicate depth by Ben Whishaw. (There is no sign of Benedict Cumberbatch, but the smart money says he cameos at some point as Rinka the great dane, killed – to the public’s horror – as the conspirators’ net closes around Scott).

Scott is, at first, as Thorpe notes, “a very heaven”. Scott idolises Thorpe, who gives him a flat, money and a nickname – Bunny – that will one day be known, as nicknames between lovers never should, nationwide. Scott becomes resentful of the time Thorpe spends away from him and fixates on his refusal to get him a new insurance card so he can claim benefits and secure his prescription medications. When their relationship disintegrates past the point of no return, Scott tells the police Thorpe made him “a victim of his lusts” and provides private letters as evidence. “Bunnies can and will go to Paris!” says one that encloses tickets to France. “That’s proof enough, isn’t it?” says Scott, who is quite as astute as Thorpe in his own way. It is passed from the Met to Scotland Yard to Special Branch and finally to MI5, where a wise man places it silently in a safe and waits for its time to come.

By the end of the first episode, it nearly has. Thorpe’s political star is rising – via several pro-European, pro-immigration and other progressive speeches that chime with the likely viewer’s likely sympathies and complicate our reactions as his mood darkens towards his ex-lover, whose proclamations are increasingly insistent, and one hellish solution to the now unheavenly body that torments him presents itself.

It is a drama as brutally funny, endlessly clever, justifiably confident as its protagonist; an immaculately-scripted hour that entwines two decades of salient political history with a finely-worked portrait of the English establishment, shaping and being shaped by a certain kind of man protected by certain privileges and labouring under a particular kind of fear. The era’s moves to legalise homosexuality and the European and immigration concerns playing out in the background give the broader moment resonance, but it is the superlative work from Jennings, Whishaw and above all Grant’s tour de force that holds it together, humanises and makes sense of it all. Bravo et encore. Bunnies can and will go to the Baftas, I’m sure.